CN109314151A - The method that back surface contact solar cell is prepared by crystalline silicon - Google Patents

The method that back surface contact solar cell is prepared by crystalline silicon Download PDF

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Publication number
CN109314151A
CN109314151A CN201780026081.4A CN201780026081A CN109314151A CN 109314151 A CN109314151 A CN 109314151A CN 201780026081 A CN201780026081 A CN 201780026081A CN 109314151 A CN109314151 A CN 109314151A
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back surface
laser
layer
contact
microns
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莫里斯·达林格尔
凯·卡斯腾斯
尤尔根·H·维尔纳
尤尔根·科勒
塞巴斯蒂安·艾西尔
托比亚斯·罗德
埃里克·霍夫曼
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Baden-Wutenberg Enbw Energy Co Ltd
EnBW Energie Baden Wuerttemberg AG
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Baden-Wutenberg Enbw Energy Co Ltd
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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
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    • H01L31/0682Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells back-junction, i.e. rearside emitter, solar cells, e.g. interdigitated base-emitter regions back-junction cells
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02Details
    • H01L31/02002Arrangements for conducting electric current to or from the device in operations
    • H01L31/02005Arrangements for conducting electric current to or from the device in operations for device characterised by at least one potential jump barrier or surface barrier
    • H01L31/02008Arrangements for conducting electric current to or from the device in operations for device characterised by at least one potential jump barrier or surface barrier for solar cells or solar cell modules
    • H01L31/0201Arrangements for conducting electric current to or from the device in operations for device characterised by at least one potential jump barrier or surface barrier for solar cells or solar cell modules comprising specially adapted module bus-bar structures
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02Details
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    • H01L31/02161Coatings for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/02167Coatings for devices characterised by at least one potential jump barrier or surface barrier for solar cells
    • H01L31/02168Coatings for devices characterised by at least one potential jump barrier or surface barrier for solar cells the coatings being antireflective or having enhancing optical properties for the solar cells
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/036Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes
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    • H01L31/18Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/186Particular post-treatment for the devices, e.g. annealing, impurity gettering, short-circuit elimination, recrystallisation
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    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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    • Y02E10/50Photovoltaic [PV] energy
    • Y02E10/546Polycrystalline silicon PV cells
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    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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Abstract

Back surface contact solar cell (10) includes wafer (16), it has anti-reflection coating (12) on the front surface, there is transmitter (20) and back surface field (32) on the back surface, and with the contact (28) generated on the back surface by laser ablation, wherein maximum spacing is 800 microns.The invention further relates to the methods for the solar battery (10) for preparing the type.

Description

The method that back surface contact solar cell is prepared by crystalline silicon
Technical field
The present invention relates to a kind of methods for preparing back surface contact solar cell by crystalline silicon.
Background technique
Known preparation method generates n doping and p doped region and the gold for contacting vapor deposition using furnace diffusion Belong to.Masks doped region needed for back surface contact solar cell structuring manufacture in and metallization in all It is required.Due to the anywhere temperature all having the same of the Silicon Wafer in diffusion furnace, on the whole surface uniformly It spreads on ground.For each diffusion, the area n and the area p on solar battery back surface generate the item or point knot of different doping Therefore structure needs the local etching step after mask (it inhibits the inside diffusion of dopant atom) or diffusion, to remove not The region of diffusion.In both cases, it requires to apply diffusion inhibition mask layer or anti-etching shielding layer, high-resolution knot Structure is also such.Since boron diffusion and phosphorus diffusion must be carried out locally, these steps are needed before furnace diffusion occurs, and And it must also highly precisely complete relative to each other.In addition, opening needs for the back surface passivation layer of contact solar cell Very high precision is wanted, so that needing lithography step.In addition, applying hard contact needs at least one lithography step.If used Two different metals then need two lithography steps.
It is uneconomic for preparing back surface contact solar cell by using mask due to the above reasons,.
According to 2007/081510 A2 of WO, back surface contact solar cell is made of crystalline silicon, wherein being used for then The precursor layer of furnace diffusion is printed by silk-screen printing or carry out portion of ink jet printing office.
It is this to prepare the inexact matching for leading to doped region, so as to cause bad efficiency.
Known prepared on solid by laser doping has height nothing from the principle of 10 2,004 036 220 A1 of DE The doped region of defect.Firstly, contacting the medium containing dopant with the surface of solids.Then position is made by laser pulse radiation In with the zone melting a bit of time of the solid of the lower face of media contact so that dopant is diffused into fusing It recrystallizes in region and when melting range is cooling without defect.
It in principle, in this way can be to avoid the masks and lithography step for using furnace diffusion to be doped.? The problem of simple and cost-effective contact is carried out on the back surface of solar battery still has.
It is known from WO2015/071217A1 to generate doped region using laser doping method.It is sudden and violent by laser ablation Reveal the contact surface on solar battery back surface, then by screen printed contacts (referring to M.Dahlinger et al., " Laser-Doped Back-Contact Solar Cells ", IEEE Journal of Photovoltaics, volume 5, No.3, in May, 2015, the 812-818 pages;With M.Dahlinger et al., " Laser Doped Screen-printed Back Contact Solar Cells Exceeding 21%Efficiency ", Energy Procedia, volume 55,2014 9 Month, the 410-415 pages).
Although silk-screen printing is method a kind of cost-effective and by verifying, height cannot be obtained by silk-screen printing Precision, therefore efficiency is restricted.In addition, the compound of electric load is greater than for example using PVD (physics during silk-screen printing Vapor deposition) deposition contact.
From WO2006/042698A1 it is known that for the contact in back surface contact solar cell, first in back surface Upper generation metal layer, then deposition etch barrier layer, then removes the etch stop layer by laser selective, finally, It is obtained using etching step electrically separated between not homopolarity.
It is important, however, that it is expected higher efficiency.
According to WO2015/047952A1, apply metal foil for contacting.Foil is welded by laser selective and in difference Pole between separate.
This method is time-consuming and expensive very much.
According to P.Verlinden et al., " High Efficiency Large Area Back Contact Concentrator Solar Cells with a Multilevel Interconnection ", International Journal of Solar Energy, 1988, volume 6, the 347-366 pages, it is known to use anode oxidation method is in back surface Contact is generated in contact solar cell.Due to multiple steps including different lithography steps, this method is extremely complex.
Finally, it is known that passing through laser transfer process transfer doping material or conduction material from 2016/0020343 A1 of US Material, such as to generate the finger for contact.
Transfer using laser transfer is some complicated processes.In addition, it is expected that higher efficiency.Also, laser transfer It is normally limited to seed layer, the i.e. thin layer of tens nanometer thickness.These are unsuitable for transmitting the metallization of electric current, and usually It must then be made significantly thicker, this needs additional method and step.
Summary of the invention
In view of this background, general object of the present invention is to provide one kind and prepares back surface contact solar-electricity by crystalline silicon The method in pond, this method allow to carry out most simple and generally the least expensive production with high quality and maximum possible efficiency.
The purpose realizes that this method has following by using the method for preparing back surface contact solar cell by crystal Step:
(a) it adulterates, preferably by laser doping, for generating the region of n doping or p doping;
(b) preferably by laser ablation, the exposed contact surface on solar battery back surface;
(c) apply metal layer in the back surface of solar battery;With,
(d) metal layer is constructed by laser ablation to prepare hard contact, the pitch is at most 800 microns.
Entire purpose of the invention is realized in this way.
Due to using the laser ablation step according to (d) to prepare contact on the back surface of solar battery, due to high-precision Degree, be obtained up to 800 microns, preferably up to 500 microns, more preferably up to 100 microns, and particularly preferably at most 60 microns Small spacing.For example, spacing can be about 50 microns.
Accord with the present invention it has been found that efficiency increases as spacing reduces.
In order to allow spacing as small as possible, other steps during the preparation of solar battery, such as doped region Preparation and contact surface exposure, lithography step and masks should be avoided as far as possible, and printing technology should be avoided, with provide The overall precision of maximum possible.Laser technology is preferred for each of these steps.
Precision when laser used according to calibration, spacing have lower limit.Lower limit is about 5 microns of spacing.
It should be understood that term " solar battery " should be understood with broad sense.It further includes special shape, such as photocell.
In yet another embodiment of the present invention, it after step (c), is firstly applied in step (d) by selectivity The resistant layer of ground removal, and hard contact electrically isolated from one is wherein generated using subsequent etching step.
In this way, it is therefore prevented that the short circuit between adjacent contacts, without since laser penetration is too during ablation Risk that is deep and leading to damage.
In an alternate embodiment of the method for the present invention, applies aluminium layer in step (c), then apply anti-anodic oxygen The layer of change, the layer of the anti-anodic oxidation passes through laser mode selectively ablation in subsequent step (d), then in ablated region Complete anodic oxidation in domain.
In this way, instead of completely removing remaining aluminium between consecutive roots, the complete conversion to aluminium oxide is obtained, this Equally it is reliably prevented short circuit.
Remaining otherwise planar surface area obtains certain advantage.
In another improvement of the invention, hard contact is connected using bus, and bus includes chaff, is passed through Laser welding is contacted by least one plug-in type dielectric layer.
First embodiment according to the present invention, anodic oxidation aluminum foil strip are used to prepare bus.For each pole, Laser Welding Termination process is occurred by separation layer.
Of course, it is possible to using different dielectric layer or stack layer to be used to be isolated on chaff or on the back surface of wafer.
Laser doping step is preferred for preparing p-type transmitter and/or for preparing n on the back surface of solar battery Back surface field (BSF).
Thus, it is preferable that the precursor layer comprising dopant, especially boron, aluminium or gallium is preferably deposited solar battery Back surface on, and by generating p-type emitter using partial radiation by means of pulse laser.
Alternatively, dopant can be used, the especially ion implanting of boron, aluminium or gallium locally generates p-type transmitter.
In this way it is possible to accurately create transmitter and not need mask or lithography step.
Another embodiment according to the present invention is formed during being adulterated by the transmitter of laser emission using light beam Or by the way that bigger doping is locally generated using the laser beam that another is independently focused under transmitter contact surface.In light During beam is formed, it is important to which pulse energy density locally increases in contact region, to obtain higher doping there.Accordingly Light beam formed and can for example be occurred using diffraction optical element.
This allows to carry out especially low-loss contact in a simple manner.
Pulse laser is preferred for laser doping, preferably with the pulse duration of 30 nanoseconds to 500 nanoseconds, further It is preferred that with 500 to 600 nanometers of wavelength, further preferably with the pulse recurrence rate of 1kHz to 2MHz.Further preferred arteries and veins Rushing energy density is 1J/cm2To 5J/cm2
Lead to the best match with doping using this laser.It can local heating silicon face and precursor in this way Layer, until can locally execute doping process within the shortest time to desired depth, wherein excess can be prevented simultaneously Doping.Using the localized variation of pulse energy density, can contact area and not in contact with emitter region in simultaneously most Doping is adjusted goodly.
Laser beam is formed on the XY of rectangular area preferably by means of optical element, and laser and substrate are relative to that This is incrementally moved with interval L, to adulterate predetermined surface.
In this way it is possible to generate accurate doping in rectangular area or linear region.
In this case, width X is preferably 0.02 to 2 millimeter, and length Y is preferably 5 microns to 500 microns.
The interval L that substrate and laser incrementally move relative to each other is preferably between 0.1Y and Y.Pass through repetition Radiation and the mobile interval L of mobile Silicon Wafer or the laser beam by being formed on the surface in the Y direction adulterate the whole of item or point A desired surface region..
In being advantageously improved at of the invention one, in order to generate n back surface field on the back surface of solar battery (BSF), it is used as precursor deposition on substrate for phosphosilicate glass layer (PSG) first, is then mixed by laser emission with generating n It is miscellaneous.The front surface doping (front-surface field, FSF) of wafer in PSG layers of deposition and high temperature dispersing furnace occurs simultaneously.The production of FSF The raw passivation for allowing to improve solar battery front surface.
, it is preferable to use etching removal phosphosilicate glass layer, is then etched back on substrate back surface after laser doping At least part of phosphorus doping layer.
According to depth and phosphorus concentration, eatch-back occurs in the two sides or only on the back surface of Silicon Wafer.The purpose of etchback step It is to reduce phosphorus present in boron emitter zone.The phosphorus surface concentration in emitter region can be adjusted by etchback step, so that After subsequent thermal oxide, boron surface concentration is than greatly at least five times of phosphorus surface concentration.
If front surface is excessively high adulterated with phosphorus, the phosphorus concentration in front surface must be reduced.The object here be so that After the FSF that subsequent use is prepared in this way carries out optimal front surface passivation step of thermal oxidation, surface phosphorus concentration It is about 11018cm-3To 11020cm-3.In addition, Silicon Wafer undergoes chemically cleaning due to eatch-back.
After BSF layers of laser doping or after local etchback step, at 700 DEG C to 1100 DEG C, preferably 800 DEG C extremely Thermal oxide is carried out in the range of 1050 DEG C.
It is this it is so-called drive in step, silica is grown as surface passivation.Further, since high temperature, doping Agent atom diffuses further into Silicon Wafer.Therefore, the surface concentration of doping is in solar battery transmitter and BSF and FSF All decline.
In another preferred embodiment of the invention, anti-reflecting layer deposit on the front surface, preferably by it is equal from Daughter enhances the silicon nitride layer of chemical vapor deposition (PECVD) deposition.
The stack layer made of low silicon and high silicon silicon or silicon nitride is preferably deposited the back surface of solar battery On, preferably deposited by PECVD.
Low silicon layer preferably has low-refraction (n < 1.7) and the thickness between 70 nanometers and 300 nanometers, and then High silicon layer is preferably the layer of layer with a high refractive index (n > 2.7) and the thickness between 10 nanometers and 100 nanometers.Two layers can To be deposited one by one in same process step in the same system.Among other things, they increase " light capture " simultaneously Make back surface passivation.In addition, high refracting layer is used as ablation mask step in subsequent process steps.
After applying stack layer, the ablation region to be contacted with exposure is preferably carried out by UV laser, wherein it is preferred that The ground high silicon layer that only ablation finally deposits in region to be contacted, this is because only they absorb UV radiation.Low silicon layer pair It is transparent for radiating in UV, therefore cannot be absorbed, therefore prevent its ablation.
Then the rest layers down to silicon interface can be etched away for subsequent contact.
In this way, contact surface is locally opened and is not had laser damage at silicon interface.
Before adulterating transmitter, front surface texture preferably is generated in the front surface of solar battery.This can be used The humidifying optical polishing of substrate in front surface and texture etching are to realize.
Humidifying optical polishing can be used as first step progress, and in the necessary situation on side, then this is in side Upper progress wet-chemical texture etching.The sequence also can change, and progress wet-chemical texture etching first is to generate solar battery Front surface texture, then carry out solar battery back surface unilateral humidifying optical polishing and solar battery back surface on containing The deposition of boron precursor layer.
The back surface contact solar cell made of crystalline silicon prepared according to preceding method includes: to have on the front surface There is the wafer of anti-reflecting layer, transmitter and base region (back surface field) on the back surface, and by being laser-ablated in back The contact generated on surface, the pitch are at most 800 microns.Spacing is preferably significant smaller, such as at 100 microns or smaller In range, for example, about 50 microns.
This generates high efficiency.In addition, reducing to the part BSF fBSFDependence.
It should be appreciated that previously cited feature of the invention and the feature of the invention to be explained further below not only can be with Provided specific combination uses, but also can be with other combinations or by themselves using without departing from model of the invention It encloses.
Detailed description of the invention
Other features and advantages of the present invention are obtained by the description of following preferred illustrative embodiment with reference to attached drawing.
Fig. 1 is the simplification section of solar battery of the present invention.
Fig. 2 is the schematic top plan view according to the element cell of the solar battery back surface of Fig. 1.
Fig. 3 a-f is depicted for different wafer qualities, according to the part the BSF f of solar batteryBSFWith the solar energy of spacing p The efficiency of battery;With,
Fig. 4 is the schematic diagram connected by pad by chaff contact.
Specific embodiment
Fig. 1 schematically depicts the section of solar battery of the invention, is generally identified with number 10.
Solar battery 10 has n-type silicon wafer 16.The front surface of Silicon Wafer is provided with the passivation on pyramid shape texture Anti-reflecting layer 12.It is front surface phosphorus-diffused layer, front-surface field (FSF) 14 below.
On its back surface, solar battery 10 has the boron emitter zone 20 of laser doping, has on the boron emitter zone There is transmitter 18, each transmitter is adulterated with selection intensity, and contact 28 is applied on the transmitter.
In addition, being arranged on the back surface of solar battery 10 by the base region 22 that phosphorus carries out laser doping.Using blunt Change layer 24, back surface is isolated with contact 28, and the transmitter 18 of selective doping is contacted by contact 28, is then generated highly doped Base region 22.
Fig. 2 is the schematic top plan view according to the element cell of the back surface of the solar battery 10 of Fig. 1.Element cell is being schemed Top and bottom continued with mirror image.Solar battery edge is located at left and right side.30 indicate base contact area.22 indicate The base region generated by BSF (back surface field) doping.34 indicate the doping of bus.20 indicate transmitter doping.Figure 18 indicates choosing The transmitter of selecting property higher-doped.Finally, 36 indicate transmitter contact zone.
So-called " spacing " refers to that (spacing is also the sun to the distance between two adjacent transmitters 18 in some sense " period " of energy battery).Fig. 1 indicates spacing with p.
Fig. 3 a-f is shown especially for different wafers, according to spacing p and BSF part fBSF(the surface element of Ohmic contact Point (base region 22, BSF doping)) solar battery relative efficiency and total surface area (base region 22 adds transmitter 18) between Relationship.Here ρ represents the specific resistance of wafer, and τ represents the volume service life of a small number of electric load.
This shows that spacing p is smaller, and relative efficiency η is bigger, and unrelated with the specific resistance of wafer and volume service life.Separately Outside, spacing p is smaller, to the part BSF fBSFDependence it is lower.According to the part BSF fBSF, larger smooth with lesser spacing p Away from the significant maximum value at p.Spacing p be 50 microns when, actually no longer with the part BSF fBSFThere is relationship.
According to the present invention, the efficiency of maximum possible is obtained using this relationship with spacing p.
According to the present invention, using laser technology, spacing < 800 micron can be prepared in a manner of technically relatively simple, it is excellent < 100 microns of choosing, more preferably < 60 microns of solar battery 10.In general, spacing is greater than 5 microns.
The preparation of this solar battery 10 is described more fully below.
Method of the invention carries out in the case where no any mask step.On the contrary, using laser doping step and swashing Light assisted ablation step opens back surface passivation layer.The laser doping for being used to prepare transmitter is also optionally injected by local ion Step replaces.During preparation is for the contact 28 of transmitter 18 and base region 22, further laser ablation step is used.
The n-type silicon wafer of base implant is used to prepare solar battery 10.
Firstly, the front surface experience wet-chemical alkalinity of solar battery 10 is textured to generate pyramid shape veining table Face.Then, the back surface of solar battery 10 is subjected to humidifying optical polishing (alkali or acid).Then in the back surface of solar battery 10 The precursor layer of upper deposition boracic, aluminium or gallium.The sequence of these steps also can change: humidifying optical polishing (when necessary only in side) It can first carry out, unilateral wet-chemical veining is then carried out in the front surface of solar battery 10.
For example, using sputtering system, or plasma-chemical depositing system (such as APCVD) is used, or use spin coating side Method or paint finishing can apply the precursor layer on the back surface of solar battery 10.
Then, laser doping technique is used to generate p-type transmitter on the back surface of solar battery 10.Here, laser The surface of pulse melts Silicon Wafer.Due to the high diffusivity constant in liquid silicon, during liquid phase, the doping that is present in precursor layer Until depth is about 1000 nanometers in the surface that atom diffuses into Silicon Wafer within about 100 nanoseconds, to form p-type transmitting Device.
Here it is possible to laser beam be formed on a silicon surface using optical element, so that single laser pulse melts have table The rectangular area of area XY clearly limited.Preferably 0.02 millimeter < X < 2 millimeter and 5 microns < Y < 500 micron.Here become Measure the width that X limits transmitter item or point.Due to the repetition radiation and movement of Silicon Wafer, or since what is formed on the surface swashs Light beam moves increment L in the Y direction, is doped to the whole surface region of transmitter item or point.Here preferred 0.1Y < L < Y。
In addition, generating the increased boron doping in part below transmitter bus-bar area during transmitter doping.This can be with By using light beam to be formed during laser emission or by using different, the laser beam that independently focuses and occur.In light beam During formation, it is important to which pulse energy density locally increases in contact region, to obtain bigger doping there.It can obtain It obtains corresponding light beam to be formed, for example, using diffraction optical element.
Due in the increased boron doping in transmitter bus-bar area (also referred to as selective transmitter) lower section part, realize compared with Low total series resistance, and therefore obtain the better fill factor of solar battery.Further, since under transmitter contact The increased boron doping in side part, it is compound on metal semiconductor interface to reduce electric load.Therefore, open-circuit voltage and too The efficiency of positive energy battery 10 increases.In addition, contact resistance reduces, so that total series resistance decline and fill factor rising.
During transmitter laser doping, two kinds of part doping can be completed in the case where no additional technical steps. Dopant profiles are adjusted by changing laser pulse energy metric density, thus regulating course resistance.
After laser doping transmitter 18, remaining precursor layer is removed in a manner of wet-chemical.Chemistry for this purpose Solution depends on precursor layer used.
Then then carry out clean silicon wafers 16 using hydrofluoric acid bath using hydrochloric acid-hydrogenperoxide steam generator.
As the alternative solution for the above-mentioned laser doping for using the precursor layer previously deposited, local ion note also can be used Enter step to generate the transmitter 18 of the solar battery 10 doped with boron.Pass through the activation of ion implanting and dopant atom The zero defect recrystallization of decrystallized silicon is obtained using thermal oxide as described below, is also then carrying out laser doping step Shi Jinhang.
In addition, by using the laser doping of rich phosphorus precursor layer, in the back surface of Silicon Wafer in the form of the highly doped region n It is upper to generate so-called back surface field (BSF).
For this purpose, the phosphorus silicic acid of rich phosphorus is deposited in the front surface of Silicon Wafer and back surface first in standard high temperature tube furnace Salt glassy layer.POCl3And O2For process gas.It is deposited at a temperature of between 700 DEG C and 850 DEG C and carries out.In addition, some phosphorus Diffusion number nanometer is to 500 nanometers in Silicon Wafer.The diffusion of optimization is so that as low as possible and shallow depth is adulterated and occurred, but still produces There is rich phosphorus interface in the phosphosilicate glass of raw richness phosphorus.
Rich phosphorus interface or phosphosilicate glass layer are used as the dopant source of post laser doping process.
As described in the doping of aforementioned transmitter, the surface of laser pulse melts Silicon Wafer.Due to the high diffusivity in liquid silicon Constant, during liquid phase, the phosphorus atoms being present in phosphosilicate glass layer diffuse into Silicon Wafer within about 100 nanoseconds Surface to about 1000 nanometers depth and form the area BSF 32, i.e. the area n of high doped.As described above, used here as optics member Part forms laser beam on a silicon surface, so that it is the square of XY clearly limited that single laser pulse melts, which have surface area size, Shape region.Equally, the whole surface region of BSF item or point is using in the Y direction with interval L between Silicon Wafer and laser beam It relatively moves and gradually adulterates.In addition, identical geometrical relationship is described about transmitter doping above.
After local BSF laser doping, phosphosilicate glass layer is removed by hydrofluoric acid solution (1% to 50%).
Then, some phosphorus doping layers are at least etched back on the back surface of substrate.For this purpose, using by hydrofluoric acid, nitric acid, acetic acid About 10 nanometers to 300 nanometers of depth of phosphorus doping layer is etched back to wet chemical solution made of deionized water.The etching step Be according to Silicon Wafer two sides or only back surface depth and phosphorus concentration and occur.Eatch-back the purpose is to reduce deposit in boron emitter zone Phosphorus.
After the thermal oxide that will be described below, the boron surface concentration in emitter region should be bigger than phosphorus surface concentration At least five times.If phosphorus doping is excessively high, need to reduce the phosphorus concentration in front surface.Goal is in subsequent high temperature oxygen 110 are obtained after changing18cm-3To 11020cm-3Phosphorus surface concentration.In addition, the chemistry that etchback step provides Silicon Wafer is clear It is clean.
Then, the cleaning of first time wet-chemical is carried out using hydrochloric acid-hydrogenperoxide steam generator and subsequent hydrofluoric acid bath.
Step is driven in as so-called followed by thermal oxide.Here silicon dioxide layer is grown with surface passivation.Or Silicon nitride layer, silicon oxynitride layer or silicon carbide stack layer also can be used in person.During driving in, since (about 800 DEG C extremely for high temperature 1050 DEG C), dopant atom diffuses further into Silicon Wafer.Therefore, the surface concentration of doping is in back surface field (BSF) (base Polar region) and front-surface field (FSF) and transmitter in all decline.Obtained silicon dioxide growth is to 5 nanometers to 105 nanometers Thickness, wherein thickness in the range of 5 nanometers to 20 nanometers desirably needs in conjunction with other anti-reflection coating.
In order to reduce effective reflection of the solar radiation on the surface of solar battery 10, pass through plasma enhanced chemical Be vapor-deposited (PECVD) deposited silicon nitride layer in the front surface of solar battery 10.Here refractive index should be in 1.9 and 2.3 Between.
The aluminium layer of 1 to 50 μ m-thick is for example applied to by evaporation or cathodic sputtering to the back surface of solar battery 10 Whole surface region prepares the contact 28 on base region 22 and transmitter 18 using this layer later.
Such as by evaporation, APCVD, PECVC, CVD or cathodic sputtering, by metal cladding, semiconductor covering layer or electricity Dielectric passivation is applied to aluminium layer.This layer should be etch resistant or should only can be by one of the etchant that then uses (for example, phosphoric acid, hydrochloric acid, sodium hydroxide or potassium hydroxide) slight etching.The layer may include such as nickel, zinc, amorphous silicon or SiOx, Silicon nitride or silicon carbide.
Now, Partial ablation is carried out to the coating for being applied to aluminium layer.
In subsequent etching step, removed by means of etchant (such as phosphoric acid, hydrochloric acid, sodium hydroxide or potassium hydroxide) By means of the aluminium in the region of laser exposure, so that the contact 28 being isolated from each other generates in base regions 22 and transmitter 18.
It, can according to a kind of method modification instead of generating isolation between alternately contact area by etching removal material To generate isolation by selectively anodic aluminum oxide layer.
For this purpose, applying the layer of anti-anodic oxidation, such as SiOx, SiNx, SiCx, Si, Ni, Cu after applying aluminium layer.? The layer is optionally removed by laser ablation in subsequent step.Then by ablated area in anodic oxidation bath (such as H2SO4 Or oxalic acid) in completely anodic oxidation (in Fig. 1, the slit being retained between adjacent contacts 28 will be completely with alumina filled).
Under any circumstance, very small spacing p may be implemented by using laser technology, and can be at 100 μm The order of magnitude or even in the range of about 50 μm.As can be seen that this significantly improves efficiency eta from Fig. 3 a-f.
Pulse laser system in aforementioned laser doping process (referring to WO2015/071217A1 and DE102004036220A1 is incorporated herein by reference in their entirety herein).Following laser parameter is preferred for generating dopant Optimize depth distribution:
In 30 nanoseconds to the pulse duration between 500 nanoseconds,
Wavelength between 500 nanometers and 600 nanometers,
Pulse recurrence rate between 1kHz and 2MHz,
In 1J/cm2And 5J/cm2Between pulse energy density.
Alternatively, it is produced using two contacts of laser welding pole (transmitter and base stage) of the chaff made of metal foil The raw bus (bow strip) 34 for being used for other battery circuit.Chaff can be respectively Chong Die with another pole.Dielectric layer or stack layer Chaff is isolated with mutual compensating pole.
In the simplest case, using the item made of aluminium foil, aluminium foil be provided on the side towards contact 28 every From anodic oxide coating.For each pole, laser beam welding is occurred by separation layer.
Of course, it is possible to using another dielectric layer or stack layer to be used to be isolated on chaff or on the back surface of wafer.

Claims (15)

1. a kind of method for preparing back surface contact solar cell by crystalline silicon, comprising the following steps:
(a) it adulterates, preferably by laser doping, is used to prepare the region (20,22) of n doping or p doping;
(b) preferably by laser ablation, exposed contact surface (26) on the back surface of the solar battery (10);
(c) apply metal layer in the back surface of the solar battery;With,
(d) by metal layer described in laser ablation to prepare hard contact (28), the pitch is at most 800 microns.
2. according to the method described in claim 1, wherein preparing the doped region (20,22) using laser doping.
3. more preferably up to 100 is micro- according to the method described in claim 1, wherein the spacing (p) is at most 500 microns Rice is particularly preferably at most 60 microns.
4. method according to claim 1 or 2, wherein the spacing (p) is at least 5 microns.
5. method according to any of the preceding claims, wherein apply resistant layer first after step (c), The resistant layer is selectively removed in step (d), and wherein using subsequent etching step generate each other electricity every From the hard contact.
6. method according to claim 1 to 4 then applies anti-sun wherein applying aluminium layer in step (c) Polarized layer, the layer of the anti-anodization passes through laser mode selectively ablation in subsequent step (d), then described Complete anodization in ablated area.
7. method according to any of the preceding claims, wherein the hard contact (28) is connected using bus (34) It connects, the bus includes chaff, and the chaff is connect using laser welding by least one plug-in type dielectric layer Touching.
8. according to the method described in claim 7, wherein the item made of anodization aluminium foil is used to prepare the bus (34).
9. method according to any of the preceding claims, wherein laser doping step is used to prepare p-type transmitter (20) and/or the back surface in the solar battery (10) prepares N-shaped back surface field BSF (22).
10. method according to any of the preceding claims, wherein on the back surface of the solar battery (10) The precursor layer containing dopant is deposited, and, p-type transmitter (20) are generated using partial radiation by pulse laser, it is described to mix Miscellaneous dose is especially boron, aluminium or gallium.
11. method according to any one of claim 1 to 9, wherein by dopant, especially boron, aluminium or gallium make P-type transmitter (20) are locally generated with ion implanting.
12. a kind of back surface contact solar cell, prepares advantageously according to any one of preceding claims, the back table Face contact solar cell has wafer (16), and the wafer (16) has anti-reflecting layer (12) on the front surface, in the back There are emitter zone (20) and base region (back surface field) (22) on surface, and have on the back surface and burnt by laser The contact (28) of preparation is lost, the pitch (p) is at most 800 microns.
13. solar battery according to claim 12, wherein the spacing (p) is at most 500 microns, more preferably extremely More 100 microns, be particularly preferably at most 60 microns, wherein preferably at most 5 microns of the spacing (p).
14. solar battery according to claim 12 or 13, wherein base region (22) and emitter region (18) Contact (28) use bus made of chaff (34) and connect, the bus (34) use Laser Welding contact (38) It is electrically connected by dielectric layer.
15. solar battery according to claim 14, wherein the chaff (34) includes anodization aluminium foil.
CN201780026081.4A 2016-04-27 2017-04-12 The method that back surface contact solar cell is prepared by crystalline silicon Pending CN109314151A (en)

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